Photographic emulsions containing tanning developing agents



United States ?atent O PHOTOGRAPHIC EMULSIONS CONTAINING TANNING DEVELOPING AGENTS llmari F. Salminen, James A. Van Allan, and Edward C. Yackel, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application April 5, 1955, Serial No. 499,504

6 Claims. (Cl. 95-6) This invention relates to light-sensitive gelatino-silver halide emulsions of use in photography and particularly to substantially unhardened gelatino-silver halide emulsions of use in photographic processes requiring the preparation of locally hardened or tanned silver halide emulsion layers.

Many silver halide developing agents are known, the oxidation products of which produced in the photographic development process possess the property of hardening or tanning gelatin emulsion layers in the region of exposure to light. Such silver halide developing agents are also known to vary in their activity as gelatin tanning silver halide developing agents. Furthermore, some silver halide developing agents, such as hydroquinone, vary appreciably in this gelatin tanning activity depending upon the conditions of usage such as sulfite concentration. Moreover, such developing agents vary widely in their stability under the optimum conditions of tanning development. For example, pyrogallol, catechol and hydroquinone are very active tanning developing agents but are comparatively unstable under the optimum conditions of usage.

In the Yackel U. S. Patent 2,592,368, granted April 8, 1952, and the Yutzy and Yackel U. S. Patent 2,596,756, granted May 13, 1952, are disclosed the catechol and hydroquinone derivatives 2,5-dihydroxydiphenyl, 3,4-dihydroxydiphenyl and 2,3-dihydroxydiphenyl which are very active as tanning developing agents for photographic processes requiring the differential tanning of unhardened gelatino-silver halide emulsion layers. These tanning developing agents, in addition to having strong tanning action, are very stable and possess the added property of being substantially insoluble in water which is favorable to their use in silver halide emulsion layers in the processes of the patents or other relief processes requiring the production of differentially tanned gelatino-silver halide emulsion layers.

We have now discovered certain derivatives of catechol which possess outstanding properties as gelatin tanning silver halide developing agents, particularly when present in unhardened gelatino-silver halide emulsion layers.

These compounds are:

A 4-phenoxy catechol, e. g.

CGHB 4-phenoxy catechol 2,751,295 Patented June 19, 1956 C uHn t n 4-(2,4-di-tert. amyl) phenoxy catechol H HC CHa H Hg 4-(2-cyclopentenyl) catechol CoHg 1,2-diethoxalyl-4-phenoxy catechol 0-0 00 OO 02H:

1,2-dlethoxalyl-4-phenyl catechol 0-0 0-0 0-0 CiHu 1,2,3-trlethoxalyl pyrogallol are very stable and may be stored for extended periods I of time without becoming hardened. This is particularly true of the compound 1,2-diethoxalyl-4-phenyl catechol. That is, this ester of 4-pheny1 catechol is distinct among other esters of 4-phenyl catechol in the respect that it is comparatively stable in photographic emulsions and does not readily hydrolyze therein, yet in the presence of alkaline solutions, such as carbonate solutions used for the developmentof emulsion layers containing the compound, the ester readily hydrolyzes to yield the corresponding gelatin tanning silver halide developing agent 4-phenyl catechol. Other esters of 4-phenyl catechol which have been investigated, such as 1,2-diacetoxy-4-phenyl catechol and 1,2-dicarbethoxy-4-phenyl catechol do not readily hydrolyze in the presence ofalkaline solutions, such as carbonate solutions, under the conditions at which it is desirable to develop the emulsion layer containing the compounds. Therefore, the latter compounds are not of use as tanning developing agents in unhardened emulsion layers.

The catechol derivatives of the invention mentioned possess the further characteristics that when they are incorporated into unhardened emulsion layers for use in preparing matrices for dye imbibition printing processes (Example 2) they yield relief images which can be dyed throughout rather than only on the surface as is characterestic of current relief image processes. A further feature of the compounds of the invention resides in the fact that they do not fog silverhalide emulsions contrary to many gelatin tanning silver halide developing agents. Naturally the developing agents of the invention also find utility in conventionally hardened silver halide emulsion layers where their high stability is of advantage. Such emulsions are useful in conventional photographic processes where differential hardening of the emulsion layer is not essential. These emulsions may be prepared in the manner of the above examples except incorporating the developing agent into a hardened or subsequently hardened emulsion. Development of the exposed emulsions is also initiated with simple alkaline solutions.

The following compounds possess some of the desirable properties indicated above but to a lesser degree and therefore are much less desirable than the mentioned compounds of the invention as tanning developing agents for use in unhardened gelatino-silver halide emulsion layers:

and

The mentioned compounds of the invention may be incorporated into gelatinosilver halide emulsion layers by means of solvents such as methyl alcohol, or higher boiling solvents such as butyl phthalate may be used for incorporating the compounds in emulsion layers as shown in the following examples:

Example 1 50 grams of 4-phenoxycatechol were dissolved in 100 grams of dibutyl phthalate by heating at about 90 C. The resulting solution was added to 550 cc. of 5 percent aqueous gelatin solution containing 4 grams of saponin at a temperature of 40 C. The resulting mixture was then passed through a colloid mill. The resulting dispersion was then added to a gelatino-silver halide emulsion containing one mol of silver halide and 560 grams of gelatin so as to obtain from about /5 to V3 mol of the developing agent per mol of silver halide in the emulsion. The emulsion was then coated onto a photographic paper base and dried.

The emulsion is particularly suitable for use in the transfer process of U. S. Patent 2,596,756 identified above, according to which the emulsion is exposed to a line or halftone subject, treated with alkaline solution to initiate development, then pressing the emulsion against an absorbent sheet to transfer a stratum of the unexposed areas to the sheet.

The other developing agents of the invention can be incorporated into an unhardened gelatino-silver halide emulsion in a similar manner.

When the emulsion is to be used in the process of the last-mentioned patent, it should contain little or no gelatin hardening agent. However, very small quantities of a gelatin hardening agent such as formaldehyde may be added if desired but only to the extent that the emulsion is no harder than a layer of photographic gelatin containing 0.25 ounce of formaldehyde (40% diluted 1:3 with water) per pound of gelatin freshly coated. The

emulsion may contain the tanning developing agents of the invention hi the amount of from about /5 to /3 mol or less of developing agent per mol of silver halide in the emulsion. The amount of gelatin in the emulsion can be varied within rather wide limits, depending somewhat upon the particnlar process in which the unhardened emulsion layer is to be used. The useful range is from about 300 to 1000 grams of gelatin per mol of silver halide in the emulsion.

The emulsions of the invention may contain, in addition to gelatin as the colloid vehicle, a dispersion of a synthetic polymer such as an ethyl acrylate-acrylonitrile copolymer. Such emulsions may be prepared as described in the Yackel U. S. Patent 2,685,510, granted August 3, 1954, substituting one of the four mentioned tanning developing agents of the invention for 4-phenyl cathechol in the procedure of the patent. emulsion is particularly useful in the silk screen process described by said patent.

The emulsions of the invention may contain in addition to the indicated tanning developing agent such as 4-phenoxy catechol, a second silver halide developing agent which possesses substantially different or no activity as a gelatin tanning silver halide developing agent, e. g., pyrogallol dimethyl ether, 4-methoxy-a-naphthol or 8- hydroxy-e-naphthol. The preparation of such emulsions can be carried out according to the procedure described in the Yutzy and Yackel U. Sv patent application Serial No. 267,447, now U. S. Patent No. 2,716,059, filed January 21, 1952, 4-phenoxy catechol, for example, being substituted for 4-phenyl catechol in the procedures shown in that invention.

The emulsions of the invention are very useful in the preparation of continuous tone gelatin relief images for use in the well known dye imbibition printing processes wherein color-separation negatives-are prepared in a Well known manner, then each negative is printed onto a film of our invention having an unhardened gelatino-silver halide emulsion layer, followed by washing out the un- I exposed emulsion areas, dyeing the resulting positive gelatin matrices and making imbibition dye prints therefrom. In a variation of this procedure, the unhardened gelatino-silver halide emulsion layers of the invention containing the indicated developing agents may be exposed directly to a colored subject such as a positive color transparency and the gelatin color-separation matrices are prepared therefrom by reversal methods. The utility of the developing agents of the invention in unhardened gelatino-silver halide emulsions for the preparation of gelatin matrices for imbibition dye printing color proc-' esses is illustrated in the following examples:

Example 2 To an unhardened gelatino-bromoiodide emulsion containing 1 mole of silver halide was added 15 grams of 4-phenoxy catechol in 750 cc. of methyl alcohol. The emulsion was coated onto a film support at a coverage of one mole of silver halide per 350 sq. ft. of surface. The coating was exposed under a film negative, developed in sodium carbonate solution for 2 minutes and the un- The resulting tanned gelatin image was removed with hot water. The resulting gelatin matrix was dyed and a dye image trans ferred therefrom by imbibition to a mordanted imbibition blank. The dye image obtained had good definition.

In a similar manner 30 g. of 1,2-diethoxalyl-4-phen)-'l catechol in 1000 cc. of methyl alcohol were added to 1 mole of a gelatino-chlorobromide emulsion containing 29.5 grams of tartrazine dye. The emulsion was coated onto a film support and dye images having high definition were obtained therefrom as described immediately above also using sodium carbonate solution to initiate development of the exposed emulsion layer.

When the similar developing agents 2 ethoxy hydroquinone, lauryl gentisate and. dodecyl catechol were incorporated into gelatino-silver halide emulsions in this manner and the emulsions were exposed and processed as described in an attempt to obtain matrices it was found that after exposure of the emulsions and treatment with carbonate solution differential hardening of the emulsions was not obtained.

4-phenoxy catechol may be prepared as follows:

4-iodovemrml (I ).$ilver trifiuoroacetate was prepared by reacting a suspension of 187 g. (1.5 moles) of silver hydroxide in 500 ml. water with 177 g. (15 moles) of trifiuoroacetic acid. The water was removed on a steam bath under vacuum and the crude product placed in a Soxhlet thimble and extracted with ether. After removal of the ether, 300 g. (89%) of the purified silver trifluoroacetate was obtained.

A mixture of 110 g. (0.5 mole) of silver trifiuoroacetate and 69 g. (0.5 mole) of dry veratrol was placed in a dry, l-liter flask equipped with stirrer and dropping funnel. A solution of 127 g. (0.5 mole) of iodine was dissolved in a minimum amount of carbon tetrachloride was added through the dropping funnel during one-half hour. After stirring for two hours, the mixture was filtered and the precipitate washed with 100 ml. of carbon tetrachloride. The solvent was removed from the filtrate under reduced pressure and the residue distilled. The yield of product boiling at 152-155 C./15 mm. was 112 g. (91%).

4-phenoxycatechol dimethyl ether (ll).-A mixture of 75 g. (0.3 mole) of iodoveratrol, 70 g. (0.6 mole) of sodium phenate, and 1 g. of copper powder was placed in a 500 ml. flask equipped with strirrer, thermometer, and reflux condenser. The stirred mixture was heated to 200 C. for four hours and then poured into 500 ml. of water. The water solution was extracted with 1 l. of benzene in three portions. The benzene was removed under vacuum and the fraction boiling at 150-152 C./ 1.5 mm. was collected. The yield was 36 g. (60% 4-phenoxycatech0l (III) .To a melt prepared by heating a mixture of 72 g. (0.53 mole) of anhydrous aluminum chloride and 12 g. (0.2 mole) of sodium chloride to 120 was added, over a period of one-half hour, 15 g. (0.06 mole) of 4-phenoxycatechol dimethyl ether. The mixture was then poured into ice and hydrochloric acid and the resulting solution extracted with three 500-ml. portions of benzene. The benzene was removed under vacuum and the fraction boiling at 180-185 C./1 mm. was collected. The yield was 11 g. (85%) n 1.6030.

Analysis.-Calcd. for CizHmOs: C, 71.2; H, 4.9; Active H, 2. Found: C, 71.6; H, 5.6; Active H, 1.9.

4-(2-cyclopentenyl) catechol can be prepared as follows:

To a well stirred suspension of 188 parts of catechol and 60 parts of phosphoric acid in 900 parts of toluene was added slowly 66 parts of freshly distilled cyclopentadiene in parts of toluene. The temperature was maintained below 20 C. during the addition and at room temperature for a further 60 hours. The toluene was then removed from the purple colored solution, the residue extracted with ether, the extract dried over potassium carbonate. The solvent was then removed, and the residue subjected to distillation. After a small forerun of catechol, there was obtained 11 parts of cyclopentenyl catechol of M. P. 5255 C. The yield is low because of polymerization of the cyclopentadiene.

1,2-diethoxalyl-4-phenylcatechol can be prepared as follows:

In a suitable flask were placed successively 55.8 parts of 4-phenylcatechol, 250 volumes of dioxane, 86 parts of ethyloxalyl chloride [R. Anschutz, Ann. 254, 1 (1889)] and 78 parts of quinoline. The reaction mixture was drowned in cracked ice and stirred until the product solidified. The mixture was filtered by suction and the solid washed on the funnel with water.

The moist solid was transferred to a beaker containing volumes of methyl alcohol, stirred to a smooth paste and filtered by suction. The product was washed further with 200 volumes of methyl alcohol. A white solid melting at 69-72 C. was obtained. It was purified to a melting point of 73-74 C. by crystallization.

1,2,3-triethoxalyl pyrogallol can be prepared as follows:

In a suitable flask were placed successively 4.2 parts of pyrogallol, 30 volumes of dioxane, 14 parts of ethyloxalyl chloride and 13 parts of quinoline. The reaction mixture was drowned in ice-water. The product separated as a gum which was taken up in 300 volumes of ether. The ethereal extract was washed three times with 300-volume portions of water, the ether layer was dried over anhydrous sodium sulfate and concentrated by distillation to an oil.

Similar suitable compounds containing the ethoxalyl groups can be prepared from 4-phenoxycatechol and its derivatives, e. g., 1,2-diethoxalyl-4-phenoxycatechol can be prepared as described above by reaction of ethyloxalyl chloride with 4-phenoxycatechol and its derivatives.

What we claim is:

1. A photographic emulsion containing a mixture of silver halide and a compound selected from the class consisting of a 4-phenoxycatechol, 4-(2-cyclopentenyl) catechol, 1,2 diethoxalyl 4 phenylcatechol, 1,2,3 tri ethoxalyl pyrogallol and 1,2 diethoxalyl 4 phenoxy catechol.

2. A photographic emulsion containing a mixture of silver halide and 4-phenoxycatechol.

3. A photographic emulsion containing a mixture of silver halide and 4-(2-cyclopentenyl) catechol 4. A photographic emulsion containing a mixture of silver halide and 1,2-diethoxalayl-4-phenylcatechol.

5. A photographic emulsion containing a mixture silver halide and 1,2,3-triethoxalyl pyrogallol.

6. A photographic emulsion containing a mixture silver halide and 1,Z-diethoxalyl-4-phenoxycatechol.

No references cited. 

1. A PHOTOGRAPHIC EMULSION CONTAINING A MIXTURE OF SILVER HALIDE AND A COMPOUND SELECTED FROM THE CLASS CONSISTING OF A 4-PHENOXYCATECHOL, 4-(2-CYCLOPENTENYL) ETHOXALYL PYROGALLOL AND 1,2 - DIETHOXALYL - 4 - PHENOXY CATECHOL. 